This application relates generally to combustors and, more particularly, to gas turbine combustors.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial aero engines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC & CO).
At least some known gas turbine combustors include between 10 and 30 mixers, which mix high velocity air with liquid fuels, such as diesel fuel, or gaseous fuels, such as natural gas. These mixers usually consist of a single fuel injector located at a center of a swirler for swirling the incoming air to enhance flame stabilization and mixing. Both the fuel injector and mixer are located on a combustor dome.
The combustor includes a mixer assembly and a heat shield that facilitates protecting the dome assembly. The heat shields are cooled by impinging air on the side nearest the dome to ensure that the operating temperature of the heat shields remains within predetermined limits. The spent impingement cooling air is introduced to the combustion chamber downstream from the mixer assembly. However, because the spent impingement cooling air is channeled downstream from the mixer assembly, the spent cooling air does not effectively mix with fuel prior to entering a flame front, and as such, may adversely impact NOx emissions.